1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to communication systems (including hard disk drive (HDD) systems) having communication channels that introduce ISI (Inter-Symbol Interference) to signal transmitted therein.
2. Description of Related Art
Data communication systems have been under continual development for many years. One such type of communication system that has been of significant interest lately is a communication system that employs iterative error correction codes. Communications systems with iterative codes are often able to achieve lower bit error rates (BER) than alternative codes for a given signal to noise ratio (SNR).
A continual and primary directive in this area of development has been to try continually to lower the SNR required to achieve a given BER within a communication system. The ideal goal has been to try to reach Shannon's limit in a communication channel. Shannon's limit may be viewed as being the data rate to be used in a communication channel, having a particular SNR, that achieves error free transmission through the communication channel. In other words, the Shannon limit is the theoretical bound for channel capacity for a given modulation and code rate.
As is known, many varieties of memory storage devices (e.g. hard disk drives (HDDs)), such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Such a memory storage system (e.g., a HDD) can itself be viewed as a communication system in which information is encoded and provided via a communication channel to a storage media; the reverse direction of communication is also performed in a HDD in which data is read from the media and passed through the communication channel (e.g., sometimes referred to as a read channel in the HDD context) at which point it is decoded to makes estimates of the information that is read.
Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
Certain devices that employ hard disk drives (HDDs) are sometimes implemented within applications that employ or require streaming information. Some examples of such applications include those that perform playback of some form of digital data (e.g., digital audio or digital video information). One example of a digital audio player is a portable digital audio device that includes some type of HDD that is operable to perform playback of digital audio information that can comport with any of a wide variety of formats or standards. Even another example of such a device that is operable to perform playback of digital data (e.g., digital audio or digital video information) is a device that is designed to perform playback of digital video (e.g., a DVR (Digital Video Recorder) type device and/or a PVR (Personal Video Recorder) type device). Many modern STBs (Set Top Boxes) that are designed to provide decoded information to a display device (e.g., some type of television) also include some form or memory storage as well. Some devices are stand-alone and operate also to record and/or playback such digital information to a display device.
The speed at which the digital information is provided from the HDD or other storage means within these devices typically is provided at a very fast rate. Sometimes, the speed at which this information can be provided from the HDD or other storage means is much faster than the rate at which the playback of digital data is being performed.